Game Lag White Paper › L3 Home network

Underpowered or overheating router Router CPU / session table exhaustion

Cause ID hn-router · Primary owner External (External)

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When dozens of devices and thousands of connections pile onto a cheap router, the router itself can’t keep up.

Why Dozens of devices, plus P2P and torrent clients opening thousands of connections → Effect The router’s CPU and session table are saturated → On screen Delayed and lost packets, failed new connections

Symptoms

Stutter, Can’t connect / infinite loading, Disconnect

Factors

Packet loss, Jitter

Who’s affected

Same household

When

The longer it runs, Randomly

Owner

Primary owner External (External)

External action items

Tell players to reboot the router (temporary fix), replace the router, and clean up programs that open many connections (P2P, torrents).

On the graph

Hits a ceiling · Router CPU and connection count, RTT to the router

Where to look

Check CPU usage, connection (session) count, and number of connected devices on the router’s admin page (if the router supports it), and compare ping to the router itself before and after a reboot

Confirmed if

When connection counts are high, even ping to the router spikes or loses packets and new connections fail. After a reboot it’s fine for a while, then gets worse again

Ruled out if

Fine up to the router but bad beyond it: the connection or ISP segment

Check with

The player’s own environment

Sources

1. An Experimental Study of Home Gateway Characteristics (IMC 2010) ACM
   Home routers allow 16 to about 1,024 TCP connections to a single server port (median 135), and low-end devices may manage only a few Mbps of throughput
2. Netfilter Conntrack Sysfs variables Linux kernel
   The maximum number of entries in Linux’s connection tracking table (nf_conntrack_max) and the default timeouts for each connection state

See also

Same layer: L3 Home network

• Wi-Fi interference and weak signal
• Congested Wi-Fi channel
• Bufferbloat (router queue)
• NAT mapping expiry
• Cell tower handover (while moving)
• RRC state transition delay (mobile radio power saving)
• Weak mobile signal and dead zones
• Frequent 5G↔LTE switching (at 5G coverage edges)
• Public Wi-Fi and corporate network restrictions

Same symptom (Stutter), other layers

• Frame time spike L1 Client game process
• Client garbage collection L1 Client game process
• Synchronous loading and shader compilation on the main thread L1 Client game process
• Slow storage delays asset streaming L1 Client game process
• Rendering load from large crowds L1 Client game process
• Missing or too-short interpolation buffer L1 Client game process
• Excessive extrapolation (dead reckoning) L1 Client game process
• Fixed-timestep catch-up spiral L1 Client game process

View the interactive card with figures and simulations